10
D EFAULT MINIMUM S LOT SIZE If you have not specified a CPU reservation for a virtual machine, it is assigned a default value of 32MHz. When the memory reservation is 0, the slot size equals the virtual machine overhead. 32 MHz 69 MB VM1 VM2 VM3 VM4VM..n

20
A DMISSION CONTROL BASED ON RESERVATIONS vSphere HA uses the actual individual reservations of the virtual machines. The CPU component by summing the CPU reservations of the powered-on VMs.

21
C OMPUTING THE C URRENT F AILOVER C APACITY If you have not specified a CPU reservation for a VM, it is assigned a default value of 32MHz

22
R ESOURCES R ESERVED IS NOT U TILIZATION The Current CPU Failover Capacity is computed by subtracting the total CPU resource requirements from the total host CPU resources and dividing the result by the total host CPU resources.

23
P ERCENTAGE RESERVED ADVANCED SETTING The default CPU reservation for a VM can be changed using the das.vmcpuminmhz advanced attribute das.vmmemoryminmb defines the default memory resource value assigned to a VM

27
T HE FAILOVERHOST To ensure that spare capacity is available on a failover host, you are prevented from powering on virtual machines or using vMotion to migrate VMs to a failover host. Also, DRS does not use a failover host for load balancing If you use the Specify Failover Hosts admission control policy and designate multiple failover hosts, DRS does not attempt to enforce VM- VM affinity rules for virtual machines that are running on failover hosts.

28
S TATUS OF THE C URRENT F AILOVER H OSTS Red - The host is disconnected, in maintenance mode, or has vSphere HA errors. Green - The host is connected, not in maintenance mode, and has no vSphere HA errors. No powered-on VMs reside on the host. Yellow - The host is connected, not in maintenance mode, and has no vSphere HA errors. However, powered-on VMs reside on the host.

31
W HAT IS A S NAPSHOT ? Preserves state and data of a VM at a specific point in time Data includes virtual disks, settings, memory (optionally) Allows you to revert to a previous state Typically used by VM admins when doing changes and by backup software ESX3, ESX(i)4 had issues with deleting snapshots ESXi5 improved snapshot consolidation

50
VM WARE T OOLS ESX(i) 4 and prior – not possible to adjust time backwards ESXi 5 – Improved time sync to be more accurate and can also adjust time backwards Enable/Disable periodic sync in VMware Tools GUI, vCenter or VMX file

54
M YTH B USTED Use W32Time or NTP Do not use VMware Tools period sync

55
S UMMARY Myth 1: VMware High Availability needs to be configured, be careful with reservations and always check run-time information Myth 2:Improvements to snapshot management and locking but still performance impact Myth 3: Use Thick Eager Zeroed disks for best I/O performance Myth 4: Use W32Time or NTP to sync time instead of VMware Tools